Not really normal - but it might become understandable with more info. I had a cat who lost her mother far too early and she made me her substitute; sucked on my hands even when she was 18 years old. Did your cats lose their mother too early? It´s also possible that they find in your clothes something they want in their food - you should ask your vet.
ALL fabrics? Or wool in particular? I've forgotten the reason (they may have been weaned too early), but there's a bit about the phenomenon in The Cat Who Ate Danish Modern, a mystery novel by Lilian Jackson Braun.
I had a cat about 60 years ago who did that when she kneaded on the wool blanket on my bed.
There's some good advice here:
(It's called "wool-sucking" even if the cats are attracted to other fabrics because wool is the usual "target.")
i think its within normal, ive seen lots of cats kneading or "masaging" people. the cat is actually kneading the teat to get milk, some cats suck.
I think it's within normal too. I had a friend who's cat sucked on my shirt sleeve. He also liked to ride in cars. He'd lay across my shoulder when I drove.
Yes, Clarence I have observed the kneading behavior -- I haven't experienced the sucking behavior though. I'm enjoying reading all these responses here.
It is normal behavior for some cats. Research has shown that it has nothing to do with being weaned too early. It is just a comforting behavior that some cats continue into adulthood.
There is one possible danger if the fabric is fluffy, like some woolens; the cat can swallow the fibers, and if he/she doesn't bring the wool-ball back up in the usual way, it can cause serious intestinal problems that can only be corrected by surgery.
That's why I posted the link to suggestions for ways to stop, or slow down, the behavior. (One suggestion was to give the cat some heavy cloth small dog toys to transfer to.)
Yes, wool would be more risky. My cats nurse on my hands, and I don't own anything wool, due to living in Texas. I love it when they come to nurse. They both do it at least once a day if I'm around enough/sit still long enough.